When modulated signals are applied to an amplifier which shows nonlinearity, odd-order distortions appear at the carrier frequency. On the other hand, even-order distortions appear at harmonic bands and at baseband. If the inpedance of the drain bias circuit at baseband is high, bias voltage is modulated by the even-order distortion. Therefore new odd-order distortion appears at the carrier frequency. In this case, out-of-band radiation power is not suppressed well with an adaptive predistorter which copes with only odd-order distortions. This paper shows a model of amplifier affected by the even-order distortion. We propose an adaptive predistorter which copes with the even-order distortion.
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